Superconducting effective-mass anisotropy in Tl2Ba2CaCu2Ox

Using torque magnetometry, we have obtained a lower bound of {approximately}10{sup 5} for the anisotropy of the superconducting effective mass in a single crystal of Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub {ital x}}. This is the largest such anisotropy yet reported for a high-{Tc} material.